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We use a simple theoretical model of seasonal market participation in the presence of liquidity constraints and transaction costs to explain the ‘sell low, buy high’ puzzle in which some households do not take advantage of inter‐temporal price arbitrage through storage and sell output postharvest at prices lower than observed prices for purchases in the subsequent lean season. We test our model with data from western Kenya using maximum likelihood estimation of a multivariate sample selection model of market participation. Access to off‐farm income and credit indeed seem to influence crop sales and purchase behaviours in a manner consistent with the hypothesised patterns.

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The findings indicate that children with intellectual disabilities can be valuable informants when forensically interviewed and can provide clear guidance about the ways in which they should be interviewed.

Summary Competition between winter‐sown wheat and Viola arvensis Murray or Papaver rhoeas L. was studied in two experiments in two successive years. The effects of varying crop and weed density were modelled in terms of weed biomass over time, weed seed production and crop yield. Biomass model parameters, representing maximum weed biomass and intra‐ and interspecific competition, were obtained for different assessment dates, enabling biomass levels to be predicted during the two growing seasons. Weed biomass declined, and its maximum level was reached earlier, with increasing crop density. Intraspecific competition was higher in the absence than in the presence of crop, increasing with time and with weed density. Halving the wheat population increased June biomass of V. arvensis by 74% and of P. rhoeas by 63%. Crop yield losses with increasing weed density were greater with low than with medium and high crop populations. P. rhoeas was significantly more competitive than V. arvensis in both years. Weed biomass in 1989 responded more to reductions in crop density following the milder winter of 1988/89 than in the previous year; however crop yields were less affected in 1989 due to summer drought, restricting late weed growth and competition. Weed seed production was related to weed biomass; the progressive lowering of crop density increased seed production, and both species were very prolific in the absence of crop. By combining models, seed production could be derived for a given competitive effect on the crop. Threshold weed populations, based on low weed levels that are not economic to control, could then be equated with the accompanying weed seed production.

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BackgroundUniversal social and emotional learning interventions can produce significant practical improvements in children’s social skills and other outcomes. However, the UK evidence base remains limited.ObjectivesTo investigate the implementation, impact and cost-effectiveness of the Promoting Alternative THinking Strategies (PATHS) curriculum.DesignCluster randomised controlled trial. Primary schools (n = 45) were randomly assigned to implement PATHS or to continue with their usual provision for 2 years.SettingPrimary schools in seven local authorities in Greater Manchester.ParticipantsChildren (n = 5218) in Years 3–5 (aged 7–9 years) attending participating schools.InterventionPATHS aims to promote children’s social skills via a taught curriculum, which is delivered by the class teacher, generalisation activities and techniques, and supplementary materials for parents. Schools in the usual provision group delivered the Social and Emotional Aspects of Learning programme and related interventions.Main outcome measuresChildren’s social skills (primary outcome, assessed by the Social Skills Improvement System); pro-social behaviour and mental health difficulties (Strengths and Difficulties Questionnaire); psychological well-being, perceptions of peer and social support, and school environment (Kidscreen-27); exclusions, attendance and attainment (National Pupil Database records); and quality-adjusted life-years (QALYs) (Child Health Utility 9 Dimensions). A comprehensive implementation and process evaluation was undertaken, involving usual provision surveys, structured observations of PATHS lessons, interviews with school staff and parents, and focus groups with children.ResultsThere was tentative evidence (at ap-value of  < 0.10) that PATHS led to very small improvements in children’s social skills, perceptions of peer and social support, and reductions in exclusions immediately following implementation. A very small but statistically significant improvement in children’s psychological well-being [d = 0.12, 95% confidence interval (CI) –0.02 to 0.25;p < 0.05) was also found. No lasting improvements in any outcomes were observed at 12- or 24-month post-intervention follow-up. PATHS was implemented well, but not at the recommended frequency; our qualitative analysis revealed that this was primarily due to competing priorities and pressure to focus on the core academic curriculum. Higher levels of implementation quality and participant responsiveness were associated with significant improvements in psychological well-being. Finally, the mean incremental cost of PATHS compared with usual provision was determined to be £29.93 per child. Mean incremental QALYs were positive and statistically significant (adjusted mean 0.0019, 95% CI 0.0009 to 0.0029;p < 0.05), and the incremental net benefit of introducing PATHS was determined to be £7.64. The probability of cost-effectiveness in our base-case scenario was 88%.LimitationsModerate attrition through the course of the main trial, and significant attrition thereafter (although this was mitigated by the use of multiple imputation of missing data); suboptimal frequency of delivery of PATHS lessons.ConclusionsThe impact of PATHS was modest and limited, although that which was observed may still represent value for money. Future work should examine the possibility of further modifications to the intervention to improve goodness of fit with the English school context without compromising its efficacy, and identify whether or not particular subgroups benefit differentially from PATHS.Trial registrationCurrent Controlled Trials ISRCTN85087674 (the study protocol can be found at:www.journalslibrary.nihr.ac.uk/programmes/phr/10300601/#/).FundingThis project was funded by the National Institute for Health Research (NIHR) Public Health Research programme and will be published in full inPublic Health Research; Vol 6, No. 10. See the NIHR Journals Library website for further project information.

This randomized controlled trial (RCT) evaluated the efficacy of the Promoting Alternative Thinking Strategies curriculum (PATHS; Kusche & Greenberg, 1994) as a means to improve children's social–emotional competence (assessed via the Social Skills Improvement System (SSIS); Gresham & Elliot, 2008) and mental health outcomes (assessed via the Strengths and Difficulties Questionnaire (SDQ); Goodman, 1997). Forty-five schools in Greater Manchester, England, were randomly assigned to treatment and control groups. Allocation was balanced by proportions of children eligible for free school meals and speaking English as an additional language via minimization. Children (N = 4516) aged 7–9 years at baseline in the participating schools were the target cohort. During the two-year trial period, teachers of this cohort in schools allocated to the intervention group delivered the PATHS curriculum, while their counterparts in the control group continued their usual provision. Teachers in PATHS schools received initial training and on-going support and assistance from trained coaches. Hierarchical linear modeling of outcome data was undertaken to identify both primary (e.g., for all children) and secondary (e.g., for children classified as “at-risk”) intervention effects. A primary effect of the PATHS curriculum was found, demonstrating increases in teacher ratings of changes in children's social–emotional competence. Additionally, secondary effects of PATHS were identified, showing reductions in teacher ratings of emotional symptoms and increases in pro-social behavior and child ratings of engagement among children identified as at-risk at baseline. However, our analyses also identified primary effects favoring the usual provision group, showing reductions in teacher ratings of peer problems and emotional symptoms, and secondary effects demonstrating reductions in teacher ratings of conduct problems and child ratings of co-operation among at-risk children. Effect sizes were small in all cases. These mixed findings suggest that social and emotional learning interventions such as PATHS may not be as efficacious when implemented outside their country of origin and evaluated in independent trials.